Two-stage compressor having interengaging rotary members

ABSTRACT

A TWO-STAGED ROOTS TYPE COMPRESSOR HAVING A HOUSING SEPARATED INTO TWO COMPARTMENTS BY A PARTITION, EACH COMPARTMENT CONTAINING A WORKING CHAMBER HAVING ROTARY MATING IMPELLERS THEREIN, INLETS TO EACH MEMBER AND OUTLETS FROM EACH CHAMBER, PASSAGES IN THE PARTITION COMMUNICATING THE OUTLET OF ONE ANOTHER WITH THE INLET OF THE OTHER CHAMBER, VALVED PASSAGE IN THE PARTITION COMMUNICATING THE INLETS OF EACH CHAMBER, THE IMPELLERS OF EACH CHAMBER BEING MOUNTED ON COMMON SHAFTS.

June 1972 R. c. WEATHERSTON ETAL 3,557,374

TWO-STAGE COMPRESSOR HAVING INTERENGAGING ROTARY MEMBERS 2 Sheets-Sheet1 Filed July 24, 1970 INVENTORs GEORGE R. DURYEA ROGER C. WEATHERSTONATTORNEY June 6, 1972 R. c. WEATHERSTON ETAL ,8

TWO-STAGE COMPRESSOR HAVING INTERENGAGING RQTARY MEMBERS Filed July 24,1970 2 Sheets-Sheet 2 INVENTORS GEORGE R. DURYEA ROGER C. WEATHERSTON BYQ4 ATTORNEY United States Patent 3,667,874 TWO-STAGE COMPRESSOR HAVINGINTER- ENGAGING ROTARY MEMBERS Roger C. Weatherston, Williamsville, andGeorge R.

Duryea, Bulialo, N.Y., assignors to Cornell Aeronautical Laboratory,Inc., Bufialo, N.Y.

Filed July 24, 1970, Ser. No. 58,009 Int. Cl. F01c 1/18, 1/30 US. Cl.418-9 3 Claims ABSTRACT OF THE DISCLOSURE A two-staged Roots typecompressor having a housing separated into two compartments by apartition, each compartment containing a working chamber having rotarymating impellers therein, inlets to each chamber and outlets from eachchamber, passages in the partition communicating the outlet of onechamber with the inlet of the other chamber, a valved passage in thepartition communicating the inlets of each chamber, the impellers ofeach chamber being mounted on common shafts.

BACKGROUND OF THE INVENTION Roots type compressors performsatisfactorily at compression ratios below two; however, as thecompression ratio increases the efficiency of the compressor decreasessignificantly. Attempts to increase the efficiency of Roots typecompressors by staging two compressors in series are known. Up to acompression ratio of about 3.5 the two staged Roots type compressorsperformance is good, however, since multiple housings, timing gears,drive shafts, bearings, external piping and seals are required, themanufacturing costs are extremely high. In addition to being costly theknown two stage Roots type compressors are complex and bulky for theircapacity.

SUMMARY OF THE INVENTION The foregoing disadvantages of prior devicesare overcome according to the present invention which provides a twostaged Roots type compressor having the same number of drive shafts,bearings, timing gears that are normally incorporated in a single stagedevice.

Additionally, the present invention provides a two stage Roots typecompressor structure conduits or piping between the stages wherein allof the connections between stages are internal thereby avoiding thenecessity of external conduits or piping between the stages.

The apparatus according to the invention also incorporates valvingstructure which permits, in a simple and efficient manner, theregulation of the flow rate through the compressor.

Basically, the present invention provides a two stage Roots typecompressor having: a first stage housing, defining an interior workingchamber, a second stage housing defining an interior working chamber,first stage inlets and outlets communicating with the working chamber ofsaid first stage housing, second stage inlets and outlets communicatingwith the working chamber of said second stage housing.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of thepresent invention reference should be had to the following detaileddescription of the same, taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a cross-sectional view of the lower first stage of thecompressor according to the present invention and is taken along line1-1 of FIG. 2;

FIG. 2 is a longitudinal sectional view along line 22 of FIG. 1; and

3,667,874 Patented June 6, 1972 "ice DESCRIPTION OF 'THE PREFERREDEMBODIMENTS Referring now to the drawings, the two stage Roots typecompressor according to the invention is generally depicted by thenumeral 10 and comprises a generally annular first or low pressure stagehousing 12 which may be oblong in section as shown. The housing isflanged at 13. A curved interior wall 14 divides the first stage housinginto two sections; an inner working chamber 16 and a surrounding annulardischarge chamber 18. Wall 14 joins Wall 12 at the curved section 20which defines an inlet passage thereat which provides communicationbetween an inlet port 22 and the working chamber 16. The oppositeportion of wall 14 is open at 24 which provides communication betweenworking chamber 16 and annular discharge chamber 18. Wall 14 may haveone or more bypass ports or slots 26 therein for a purpose to bediscussed hereinbelow.

A pair of coacting multilobed Roots type impeller elements 28 and 30 aremounted on shafts 32 and 34 for rotation in chamber 16. As shown forillustrative purposes only, each impeller has three lobes.

The open ends of chambers 16 and 18 are sealingly closed by an end plate36 and an interstage partition 38. Conventional sealing rings (notillustrated) may be employed. Partition 38 has a pair of through ports40 and 42 which communicate with annular discharge chamber 18. Betweenports 40 and 42 partition 38 also contains a bypass port 44 whichcommunicates with the first stage inlet passage 20.

A valve member, illustrated schematically in FIG. 2 is adapted to seaton and close communication through port 44. As shown this valve maycomprise a frustoconical head 46, a forward piston portion 48, guides 50and a stem 52, which may pass through end plate 36 for actuation by asuitable actuator.

A second or high pressure stage housing 54 sealingly abuts partition 38.Housing 54 is similar in exterior configuration to housing 12 andcomprises an interior Working chamber 56, curved ledges 58 betweenchamber 56 and casing 54 defining a discharge slot 60 leading to anarcuate discharge region 62, curved lips 64 between chamber 56 andcasing 54 opposite ledges 58 which define a second stage inlet slot 66leading to an arcuate second stage inlet region 68. Ports 40, 42 and 44in partition 38 are in communication with the second stage inlet re gion68. An outlet port 70 is in communication with the outlet region 62.Ledge 58 contains one or more bypass ports or slots 72 similar to slots26 of the first stage.

A pair of second stage Roots type impeller elements 74 and 76 aremounted on shafts 32 and 34 for rotation in chamber 56. Impeller 74 islocated on the same shaft as impeller 30 and impeller 76 is located onthe same shaft as impeller 28 and all contain three lobes asillustrated. For a purpose to be discussed hereinbelow, it is importantto note that each one of the impellers on each of the shafts is one halfcycle out of phase with the other impeller on the same shaft. Thus,impeller 28 is one half cycle out of phase with impeller 74 and impeller30 is substantially one half cycle out of phase with impeller 76. Withthree lobes as illustrated the impellers in each stage are 60 degreesout of phase.

An end sealing plate 78 abuts and seals against one end flange 80 ofhousing 54 and thereby closes one end of chamber 56 and regions 62 and68, the other ends of which are closed by partition 38. The structure isjoined and secured by suitable fastening means illustrated at 81.

A single pair of conventional driving and timing gears 82 and 84 arelocated on shafts 32 and 34 for driving impellers 28, 30, 74 and 76.Conventional end bearings are provided at 86, '88, 90 and 92.

In operation inlet gas is drawn in through port 22, passage 20 intofirst stage working chamber 16. The gas is compressed by the action ofimpellers 28 and 30 and is discharged through opening 24 to annulardischarge chamber 18, thence through ports 40 and 42 in partition 38 tothe inlet region 68 of the second stage casing; 54'. From region 68 thegas is drawn into the second stage Working chamber 56 through opening 66where it under goes further compression by the action of impellers 74and 76 and is discharged through slot 6-0 to outlet region 62 to outletport 70 to a point of use.

If it is desirable to reduce or otherwise regulate the flow capacityvalve 46 may be actuated to permit turndown of the compressor by causinga variable portion of the gas entering second stage inlet region 68 tobe returned via port 44 to the first stage inlet opening 20. Valve 46may be operated in response to the speed of the impellers to permit anautomatic capacity turndown. Alternatively, any suitable type ofactuation could be employed.

As noted earlier, the impellers of the first stage are substantially onehalf cycle (60) out of phase with the impellers of the second stage.Thus, the vector relations of loads from the first and second stageimpellers are at a 60 angle with respect to each other and as aconsequence the maximum load is less than for the case where eachimpeller is in phase. In addition the variation in torsional loading oneach shaft is reduced and the torque requirement in the driving andtiming gears is made more uniform. With three lobe impellers asillustrated the ideal phase difference would be 120/2 or 60 degrees.With two lobes the ideal phase difierence would be 180/2 or 90' degrees.

The purpose of bypass ports 26 and 72 is to smooth out pulsations,reduce noise and augment the shaft work as disclosed in copendingapplication Ser. No. 742,890 filed July 5, 1968 for Gear Compressors andExpanders, now Pat. No. 3,531,227, and assigned to the assignee of thepresent invention.

Although a preferred embodiment of the present invention has beendescribed, changes will occur to those skilled in the art; therefore, itis intended that the scope of the present invention is to be limitedonly by the scope of the appended claims.

We claim:

1. A two-stage Roots type compressor, comprising;

(a) a first stage housing defining an interior working chamber,

(b) a second stage housing adjacent said first stage housing defining aninterior working chamber,

(c) a thin walled partition intermediate said first and second stagehousings,

(d) first stage inlets and outlets communicating with the workingchamber of said first stage housing,

(e) second stage inlet and outlets communicating with the workingchamber of said second stage housing,

(f) ports in said partition communicating said first stage outlet withsaid second stage inlet,

(g) an annular chamber surrounding said first stage working chamber, oneend of which communicates with said first stage outlet, the other end ofwhich communicates with said ports in said partition,

(11) a pair of spaced rotating shafts passing through each of saidworking chambers,

(i) mating Roots type impellers mounted on said shafts in said firststage working chamber, and

(j) mating Roots type impellers mounted on said shafts in said secondstage working chamber.

2. The compressor according to claim 1, further comprising;

(k) a turndown port in said partition communicating said second stageinlet with said first stage inlet, and

(l) a valve coacting with said turndown port.

3. The compressor according to claim 2, wherein;

(m) the impellers common to each of said shafts are substantially onehalf cycle out of phase.

References Cited UNITED STATES PATENTS 3,150,593 9/1964 Funk et al 418-9X 2,324,116 7/1943 Sivertsen 4189 X 1,531,607 371925 Green 418-92,489,887 ll/ 1949 Houghton 418-86 713,443 11/ 1902 Jewell 418-206.

FOREIGN PATENTS 2,402 9/ 1857 Great Britain 418-9 CARLTON R. CROYLE,Primary Examiner R. E. GLUCK, Assistant Examiner

